Taking place in a new location referred to as Oasis, the pack will add new missions, raids, items, weapons, bosses, rarity levels and heads for each character class.
The add-on was discovered within a Trophy patch for the Borderlands 2 'Mechromancer' DLC, which was released yesterday (October 9) on Xbox 360, PS3 and PC.
PC source files posted on ShackNews, meanwhile, describe a "prize so great, that men would turn the sands red in pursuit of it".
"Legends speak of Captain Blade's Lost Treasure of the Sands. Of a prize so great, that men would turn the sands red in pursuit of it.
"Of a pirate queen, courageous and deadly, who would stop at nothing to find it. Of a monstrous Leviathan. Of the Vault Hunters who journeyed to the desert town of Oasis, not knowing the horrors that would befall them."
Copyright: 2K GamesThe pack is likely the first of four pieces of DLC releasing between now and June 2013.
Released last month, Borderlands 2 was the biggest-selling launch of the year until the release of FIFA 13.
> Read Digital Spy's Borderlands 2 review
Watch the launch trailer for Borderlands 2 below: